The invention relates to a brake regulation system for motor vehicles with an electronic control unit, by which an automatic parking brake function can be activated when the motor vehicle is stationary and can be deactivated upon reaching a predetermined triggering condition.
Various adequate methods and devices intended for preventing vehicles from rolling away are known in particular, but not necessarily for use on slopes. In at least one operating mode in the case of an activated brake pedal or through an additional activation element, the brake force is usually held or actively built up at least at one wheel of a vehicle as a function, or independently of, the degree to which the brake pedal or another activation element is activated. At the same time, in order to activate and/or deactivate the function, different occurrence conditions and/or triggering conditions are provided jointly or alternatingly.
These methods and/or devices are known, for example, under the names “start-up assist” function, “hill assist” function, “hill hold” function, or “automatic hold” function. In summary, these methods are referred to below as an automatic parking brake function. The common feature of all of these automatic parking brake functions is, for example, a hydraulic, mechanical electrohydraulic, electromechanical or pneumatic, electronically controllable brake system, by which the holding of the vehicle and the prevention of the vehicle from starting to roll is accomplished. There also exist methods, in which the vehicle is prevented from starting to roll by means of the transmission (in particular, an automatic transmission). In all of the functions, the function is activated, for example, by activating the brake pedal or the hand brake, or by means of switching elements that are connected to said brake, and/or even other activation elements (for example, switches, push buttons, and the like). A deactivation of the function occurs by means of the same or also other auxiliary means (such as acceleration pedal position, coupling signal, drive torque signals of the engine or the like, and/or also following the expiration of a defined holding period).
Other important and necessary auxiliary measures, control signals or switching means for representing the functions are, for example, usually one or more speed signals for detecting the stationary phase of the vehicle; mechanical, pneumatic or hydraulic actuators (just as possible are, in principle, also electro-hydraulic, electro-pneumatic or electric actuators) in the wheel brakes, in particular in the feed lines to the wheel brakes, by which the braking effect can be increased, decreased, and/or can be held temporarily (for example, the control/regulating valves integrated in the form of an existing control or regulating device, for example ABS, ASC/ASR, DSC/ESP/EHB system). Optionally, longitudinal acceleration or inclination sensors are also provided, by which the roadway longitudinal inclination is determined, and from which the necessary braking power for a guaranteed immobilization of the vehicle and the start-up torque, which is necessary for the roadway inclination, can be determined. One or more pressure sensors may be provided, by which the brake pressure, in particular the generated brake torque, at the wheel brake(s) can be determined.
According to DE 10 2006 026 626, in the presence of a triggering condition, the brake pressure, which was built-up for the parking brake function at least at one driven wheel where a coefficient of friction below a predetermined threshold was determined, is converted into a brake pressure that is necessary for preventing a roll away on longitudinally inclined roadways or which is necessary for reaching a start-up, in particular through transfer into the anti-slip control at a very low coefficient of friction.
The term “brake pressure” shall also be defined as any analogous or generalizing variable indicative of brake pressure, such as the brake torque, which can be made effective by decelerating a wheel, for example, with electric, hydraulic and/or electrohydraulic means.
The object of the invention is to provide an improved brake regulation system, in particular for handling the transition from a parking brake function into a start-up process.
The invention achieves this object by providing a brake regulation system with an electronic control unit, by which an automatic parking brake function can be activated when the motor vehicle is stationary and can be deactivated upon reaching a predetermined triggering condition. The control unit can determine in a wheel selective manner the coefficient of friction of the roadway at the location of the motor vehicle, which is held so as to be stationary by way of the parking brake function. In the presence of different coefficients of friction at the right and left wheels of at least one driven axle, the triggering condition is adapted in the direction of a longer hold of the brake pressure. Advantageous further developments of the invention are described herein.
In the inventive brake regulation system for motor vehicles with an electronic control unit, by which an automatic parking brake function can be activated in the stationary phase of the motor vehicle, the automatic parking brake function can usually be deactivated upon reaching a predetermined triggering condition (for example, detection of a start-up request). The control unit, which can receive both sensor signals and data through the databus connections to other control units as input signals, can determine in a wheel selective manner the coefficient of friction (that is, the effective adhesion) between the tires and the roadway at the location of the motor vehicle, which is held in the stationary mode by the parking brake function. In so doing, the coefficient of friction (or an amount which is directly or indirectly proportional to the coefficient of friction) can be measured, calculated, estimated or sensed directly or indirectly.
According to an aspect of the invention, in the presence of different coefficients of friction at the right and left wheels of at least one driven axle, the triggering condition is adapted in the direction of a longer hold of the brake pressure.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.